United States investigators have concluded that North Korea orchestrated the late November network intrusions that compromised sensitive personal data for tens of thousands of Sony Pictures employees, according to The Wall Street Journal.

Officials are “still gathering evidence and are trying to build a clearer picture of who directed the hacking and how,” the Journal stated, citing unnamed sources “familiar with the investigation.”

ABC News also reported earlier on Tuesday that U.S. officials believed an elite North Korean hacking unit was behind the attack. Investigators traced the intrusions into Sony’s computer network, saying they were “routed through a number of infected computers in various locations overseas, including computers in Singapore, Thailand, Italy, Bolivia, Poland, and Cyprus,” ABC News reported.

Revelations about the scope of the Sony Networks hack appeared in early December when unknown hackers calling themselves the “Guardians of Peace,” or “GOP,” began posting stolen files to the Internet. Among the private data that was stolen and posted online were some 47,000 Social Security numbers belonging to Sony employees—and famous Hollywood stars.

The Journal reported that U.S. investigators “strongly suspect” that the attack was carried out by a North Korean government-backed hacking group known as Unit 121, or alternatively as Bureau 121, which is part of the government’s General Bureau of Reconnaissance and is believed to have been behind cyber attacks aimed at South Korea.

The Journal reported that U.S. officials were concerned over the diplomatic implications of revealing their findings in the Sony hack investigation.

“Within the U.S. government, there has been an internal debate in recent days about when and how to … reveal that belief publicly, because doing so could complicate relations with Japan, and raises the difficult question of how the U.S. should respond to an aggressive act by a foreign government,” the newspaper reported.

The supposed motive for North Korea was anger over The Interview, a Sony Pictures comedy in which bumbling journalists are enlisted by the CIA to assassinate North Korean leader Kim Jong-un.

Earlier this week, the GOP tied the Sony hack to outrage over The Interview.

An email purportedly sent by the Guardians of Peace warns moviegoers to “remember the 11th of September 2011,” and threatens a “bitter fate” to those who attend screenings of The Interview, which is slated to open on Dec. 25 in the United States—though Sony has reportedly considered cancelling that launch date in light of the threats.

The message, published by Fusion.net, was posted on Pastebin and was “accompanied by links to torrent files, similar to the batches sent out on several prior occasions,” Fusion.net said.